In recent years, automatic transmissions using a planetary gear having a ring gear in order to attain the speed ratios of an output member are widely used as automatic transmissions that are mounted on vehicles etc. In this type of automatic transmission, multiple speeds such as, e.g., eight forward speeds have been implemented in response to a demand for improved fuel economy etc., and automatic transmissions using a deceleration planetary gear and a shifting planetary gear are known in the art.
Such automatic transmissions are desired to be compact in view of mountability on vehicles. As a solution, there is an automatic transmission using a clutch including inner friction plates that are engaged with splines formed on the outer periphery of a ring gear of a deceleration planetary gear, outer friction plates that are placed alternately with the inner friction plates, and a hydraulic servo having a piston capable of pressing the inner friction plates from one side in the axial direction (see Patent Document 1). The outer friction plates are coupled to a sun gear of a shifting planetary gear. That is, this clutch couples and decouples the ring gear of the deceleration planetary gear to and from the sun gear of the shifting planetary gear. This automatic transmission can be made compact as the deceleration planetary gear can be placed so as to overlap the inner friction plates and the outer friction plates of the clutch in the axial direction.
In this automatic transmission, the hydraulic servo that presses the inner friction plates and the outer friction plates by the piston is contained in a clutch drum to which the outer friction plates are coupled, and the hydraulic servo is provided so as to rotate together with the sun gear of the shifting planetary gear.
In order to support the ring gear, this automatic transmission includes a substantially circular plate-shaped support member on which the ring gear is fitted. The ring gear and the support member are positioned in the axial direction by a snap ring. According to this configuration, the ring gear and the support member can be integrated by a simple configuration.